1. Field of the Invention
The present invention relates to a container vault and, more particularly, to an above-ground storage tank for flammable liquids.
2. Discussion of Background
Since the 1970s, people in the United States as well as in other parts of the world, have become increasingly concerned with the environment and the contamination of that environment, including the earth's soil, its atmosphere, and its water. The first Earth Day in 1970 resulted in the eventual creation of the Environmental Protection Agency by the United States Congress.
One of the many problems which the Environmental Protection Agency has addressed in recent years is the deterioration of large, underground storage tanks which has resulted in the leakage of contaminants into the soil. For example, the deterioration of gas station storage tanks has resulted in the leakage of gasoline and diesel fuel into the surrounding water table.
To correct this problem, the EPA has suggested that all fuel storage tanks be placed above ground. However, this has created a classic confrontation between governmental departments, since the fire departments of most major cities prefer that fuel storage tanks be placed below ground to reduce fire hazard. Most municipal codes have been drafted with this concern in mind. In more recent years, the creation of large concrete-entombed tanks has been suggested as a solution to the problem. In accordance with this suggestion, a gasoline storage tank may be entombed in concrete and placed above the ground to enable its surfaces to be easily checked for deterioration and fluid leakage. By entombing the fuel tank in concrete, the tank was thought to be impervious to impact from a vehicle that might back into it, for example, and resistant to fire due to the insulating effect of the concrete. One example of such an entombed tank is shown in U.S. Pat. No. 4,826,644, issued May 2, 1989 to T. R. Lindquist and R. Bambacigno.
The concrete entombed tank has several disadvantages, however, including cost and convenience. For example, a 1,000-gallon concrete-entombed tank weighs 18,000 pounds after it has been manufactured, and such a tank requires a large truck and crane with at least two 20-ton nylon straps to transport it to the site where it is to be used and to then place the tank in the desired position. The concrete-entombed tank is provided with bottom supporting feet to permit the inspection of its bottom surface during its use. In California, where earthquakes represent a real concern, concrete shoes are placed on the site on either side of the bottom supporting feet to prevent the movement of the tank during an earthquake. The placement of the concrete tank between the concrete shoes can be a very dangerous procedure in view of the tank's weight.
Another disadvantage of the concrete-encased tank is that the exposed concrete is subjected to environmental effects, such as varying temperatures, which eventually lead to cracking and deterioration. Because of these problems, exposed concrete typically must incorporate heavy aggregate such as stone, increasing is weight and at the same time reducing its insulating qualities.